1. Field of the Invention
This invention relates to the field of data processing systems. More particularly, this invention relates to the power control signalling within data processing systems whereby portions of a data processing system may be powered up or powered down.
2. Description of the Prior Art
It is known to provide data processing systems having multiple power domains which may be selectively powered up or powered down. As an example, a data processing system may have a CPU core which is permanently powered and separate DSP or floating point arithmetic units that are only powered when they are needed. This technique is useful in reducing the overall power consumption of a data processing system.
Whilst such power control strategies are effective in reducing power consumption, they are typically complex to design and provide as considerable care needs to be taken to ensure that the different portions of the circuit may properly close down and start up again in all appropriate circumstances. Furthermore, as circuit complexity increases, it is increasingly difficult to select and then test the points within a circuit at which the power supply should be gated and the way in which the control of the power supply to different portions of the circuit should be handled.
An additional difficulty that arises in this context is that increasing numbers of data processing circuits are being designed in high level design languages and then synthesised with appropriate tools down to gate level. Whilst such an approach has many advantages in terms of the speed of generating the designs and the way that such designs may be validated, a problem arises in that such design tools typically assume a constant unvarying power supply. These high level design language approaches and tools are ill suited to use with environments in which it is desired to selectively control the power supply to different portions of the circuit as it operates. If a high level design language is used to design a circuit and then selectable power supply functionality added by manually inserting additional circuit elements and gates, a significant problem arises in reliably verifying the design concerned.